BP said it is "generating significant cash flow" and has a "strong and valuable" oil reserve, both of which will help it survive the response to the spill.

The statement helped push BP's U.S. shares up 12.3% to close at $32.78, but its London stock closed more than 6.7% lower.

BP's shares tumbled $5.48 to $29.20 Wednesday on volume nine times above normal. The drop came amid some speculation about the company's future -- in a Fortune interview, oil analyst Matt Simmons said BP's "lawsuits, cleanup and other expenses" will force the company into bankruptcy within the month.

It's been more than seven weeks since the Deepwater Horizon rig exploded, killing 11 people and causing the oil spill.

On April 19, the day before the disaster, BP shares closed at $58.86. Since that time the stock has plunged by 50.4%.

Below book value: Even with Thursday's surge, BP shares are still trading below their book value, an important metric for investors.

The book value is a company's hard assets - in BP's case, its oil fields and rigs - minus its intangible assets and its liabilities. BP's book value is $33.25 per share.

When a stock price is trading below its book value, it shows that investors have little confidence that the company is worth even as much as its assets.

Unrealistic fears? But a report from Oppenheimer Equity Research called Wednesday's sell-off "panic selling," adding, "investors dumped BP shares on fear of unrealistically high potential liabilities."

The report said BP shares currently price in $60 billion worth of potential liabilities, "which we think is very unrealistic."

Oppenheimer also shrugged off fears that the company will go bankrupt, be acquired by a rival or fire chief executive Tony Hayward.

"Driving BP out of business would not clean the Gulf Coast, pay plaintiffs or help its 23,000 employees," the report said. "We think such action is both unnecessary and unlikely."

Dividend worries: In addition to thebankruptcy fears, there's concern about BP's quarterly dividend that is slated to be paid out June 21.

Last week, Sen. Charles Schumer, D-N.Y., and Sen. Ron Wyden, D-Ore., sent a letter to BP chief executive Tony Hayward saying it was "unfathomable that BP would pay out a dividend ... before the total cost of [the] oil spill cleanup is estimated."

Schumer and Wyden cited a Credit Suisse report that said the total cleanup cost could reach $37 billion if oil continues gushing until a relief well is completed in August.

On Tuesday, a group of 50 House Representatives sent a letter outlining similar points.

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